Modern color electrophotographic printers (laser printers) are significantly more expensive to acquire and operate than monochrome laser printers. A large component of this additional expense for color lasers is the requirement of four developing unit, as compared to a single monochrome developing unit for a monochrome laser printer. Additionally, the frequency of customer interventions to replace developing unit is generally four times higher in color laser printers as compared to monochrome laser printers.
Present color laser printers require that all four developing unit be installed and available for the printer to be operable. If one or more of the developing unit are not installed or have an insufficient supply of developing unit, an error message is generated and the printer will not operate until the problem developing unit or developing unit are replaced. This is the case even in the situation where a user desires to print only monochrome images using the monochrome developing unit which is installed and fully operable.
What is needed is a laser printer capable of full color output, but also operable with less than all four of the developing unit installed. Instead of remaining in an error state when a developing unit is missing or unavailable, the laser printer remains operable to print monochrome images or single "spot color" images using a single color and monochrome developing unit.